how do i backup and restore my iphone so it can be unlocked?

I'm not sure that will unlock your iPhone (if I understand what you mean by unlock), but here are the instructions you need:

How to back up your iPhone, iPad, and iPod touch - Apple Support

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

See javaliga’s post. But you should be backing up your phone regularly already, and you can set up iCloud to back it up automatically every night. Not just for this reason, but suppose it was lost or stolen, dropped in a toilet or got thrown under a bus? Or locked because you (or a child) entered the wrong password 10 times? Or any other disasters that you can clearly imagine?